# Impact of high spins on the ejection of mass in GW170817

## TL;DR

This paper investigates how high stellar spins influence mass ejection in neutron-star mergers, revealing that aligned high spins can suppress dynamical ejecta, affecting kilonova observations.

## Contribution

It provides the first detailed general-relativistic magnetohydrodynamic simulations showing the impact of high spins on mass ejection and composition in neutron-star mergers.

## Key findings

- High aligned spins suppress dynamical ejecta mass.
- High spins lead to more extended, colder merger remnants.
- Spin effects alter the angular distribution and composition of ejected matter.

## Abstract

Following the detection of GW170817 and the accompanying kilonova AT2017gfo, it has become crucial to model and understand the various channels through which mass is ejected in neutron-star binary mergers. We discuss the impact that high stellar spins prior to merger have on the ejection of mass focussing, in particular, on the dynamically ejected mass by performing general-relativistic magnetohydrodynamic simulations employing finite-temperature equations of state and neutrino-cooling effects. Using eight different models with dimensionless spins ranging from $\chi\simeq-0.14$ to $\chi\simeq0.29$ we discuss how the presence of different spins affects the angular distribution and composition of the ejected matter. Most importantly, we find that the dynamical component of the ejected mass can be strongly suppressed in the case of high spins aligned with the orbital angular momentum. In this case, in fact, the merger remnant has an excess angular momentum yielding a more extended and "colder" object, with reduced ability to shed mass dynamically. We discuss how this result impacts the analysis of the recent merger event GW170817 and its kilonova afterglow.